The present invention relates to computer networks and, more particularly, to management of entities in a computer network having a multi-hop peer connection topology.
Data communications in a computer network involves the exchange of data between two or more entities interconnected by communication links and subnetworks. These networks are typically software programs executing on hardware computer platforms which, depending on their roles within a network, may serve as host stations, end stations or intermediate stations. Examples of intermediate stations include routers, bridges and switches that interconnect communication links in subnetworks; an end station may be a computer located on one of the subnetworks. More generally, an end station connotes a source of or target for data that typically does not provide routing or other services to other computers on the network. A local area network (LAN) is an example of a subnetwork that provides relatively short-distance communication among the interconnected stations; in contrast, a wide area network (WAN) facilitates long-distance communication over links provided by public or private telecommunications facilities.
End stations typically communicate by exchanging discrete packets or frames of data according to predefined protocols. In this context, a protocol represents a set of rules defining how the stations interact with each other to transfer data. Such interaction is simple within a LAN, since these are typically xe2x80x9cmulticastxe2x80x9d networks: when a source station transmits a frame over the LAN, it reaches all stations on that LAN. If the intended recipient of the frame is connected to another LAN, the frame is passed over a routing device to that other LAN. Collectively, these hardware and software components comprise a communications network and their interconnections are defined by an underlying architecture.
Most computer network architectures are organized as a series of hardware and software levels or xe2x80x9clayersxe2x80x9d within each station. These layers interact to format data for transfer between, e.g., a source station and a destination station communicating over the network. Specifically, predetermined services are performed on that data as it passed through each layer, and the layers communicate with each other by means of the predefined protocols. This design permits each layer to offer selected services to other layers using a standardized interface that shields the other layers from details of actual implementation of the services. The lower layers of these architectures are generally standardized and implemented in hardware and firmware, whereas the higher layers are usually implemented in the form of software. Examples of such communications architectures include the System Network Architecture (SNA) developed by International Business Machines (IBM) Corporation and the Internet Communications Architecture.
The Internet architecture is represented by four layers termed, in ascending interfacing order, the network interface, internetwork, transport and application layers. The primary internetwork layer protocol of the Internet architecture is the Internet Protocol (IP). IP is primarily a connectionless protocol that provides for internetworking routing, fragmentation and reassembly of exchanged packets-generally referred to as xe2x80x9cdatagramsxe2x80x9d in an Internet environment-and which relies on transport protocols for end-to-end reliability. An example of such a transport protocol is the Transmission Control Protocol (TCP), which is implemented by the transport layer and provides connection-oriented services to the upper layer protocols of the Internet architecture. The term TCP/IP is commonly used to denote this architecture; the TCP/IP architecture is discussed in Computer Networks, 3rd edition, by Andrew S. Tanenbaum, published by Prentice-Hall, PTR in 1996, all disclosures of which are incorporated herein by reference, particularly at pages 28-54.
SNA is a communications framework widely used to define network functions and establish standards for enabling different models of IBM computer to exchange and process data. SNA is essentially a design philosophy that separates network communications into several layers termed, in ascending order, the physical control, the data link control, the path control, the transmission control, the data flow control, the presentation services and the transaction services layers. Each of these layers represents a graduated level of fimction moving upward from physical connections to application software.
In the SNA architecture, the data link control layer is responsible for transmission of data from one end station to another. Bridges or devices in the data link control layer are used to connect two or more LANs so that end stations on either LAN are allowed to access resources on the LANs. Connection-oriented services at the data link layer generally involve three distinct phases: connection establishment, data transfer and connection termination. During connection establishment, a single path or connection, e.g., an IEEE 802.2 logical link control type 2 (LLC2) connection, is established between the source and destination stations. Once the connection has been established, data is transferred sequentially over the path and, when the LLC2 connection is no longer needed, the path is terminated. Reliable communication of the LLC2 is well known and described by Andrew Tanenbaum in his book Computer Networks, Second Edition, published in 1988, all disclosures of which are incorporated herein by reference, especially at pages 253-257.
FIG. 1 is a schematic block diagram of a conventional computer network 100 having a host computer coupled to a Token Ring (TR) network TR1 and an end station coupled to TR2. The TR networks are of the type that support Source/Route Bridging (SRB) operations with respect to the contents of a routing information field (RIF) of a frame. The host computer is preferably a SNA host entity comprising a mainframe computer 110 coupled to a channel-attached router or front end processor (FEP), hereinafter referred to as the xe2x80x9chost network connectionxe2x80x9d 112; in addition, the end station is a xe2x80x9cphysical unitxe2x80x9d (PU) SNA entity 114. An SRB bridging device B1 interconnects TR1 and TR2 such that the SRB network 100 effectively functions as a LAN.
The PU communicates with the host by exchanging TR frames over LLC2 connections or sessions through the SRB network. Each TR frame 120 includes a RIF 122 that contains source route information in the form of ring number/bridge number pair xe2x80x9chopsxe2x80x9d within a path between the stations. For example, the RIF 122 of TR frame 120 transmitted by the PU to host contains [0021.0010]. An LLC2 session is established between the stations using a special TR frame, called an explorer frame.
The explorer frame is used by a source (PU) to xe2x80x9cdiscoverxe2x80x9d the path to a destination (host); thereafter, a Set Asynchronous Balanced Mode Extended (SABME) frame is sent from the PU to the host to establish a logical connection between the end stations, and the host responds to the SABME frame with an Unnumbered Acknowledgment (UA) frame. Once the UA frame is received by the PU, a connection is established between the source and destination, and these stations communicate by exchanging TR information (INFO) and acknowledgment frames until the logical link SNA session is completed.
For example, the PU transmits an INFO frame over TR2 and through BR1 and TR1 to the host. Upon successfully receiving the INFO frame, the host responds by transmitting an LLC2 Receive/Ready (RR) acknowledgment frame over the SRB network to the PU. This INFO/RR exchange continues until the PU has successfully transmitted all of its data and the host has successfully received all of that data. Session completion is then initiated by a Disconnected Mode (DM) frame being transmitted from the PU to the host; the disconnection is thereafter acknowledged by the host responding with a UA frame. The LLC2 frames (packets) are described by Radia Perlman in her book Interconnections, Bridges and Routers, published by Addison Wellesly Publishing Company, in 1992, all disclosures in which are incorporated herein by reference, particularly at pages 33-34.
As noted, each TR INFO frame sent from a source to a destination is acknowledged by an RR frame; if the source end station does not receive the acknowledgment frame within a prescribed period of time, a xe2x80x9ctime-outxe2x80x9d may occur and the source sends a DM frame to prematurely terminate the session. Since network 100 is a LAN, it facilitates fast transfer of information between its connected stations and, as a result, a time-out condition should rarely occur. If a WAN such as a TCP/IP cloud is disposed within a LAN-based network, it is likely that a time-out will arise because of the latencies introduced by the TCP/IP cloud. That is, a frame traversing the WAN cloud incurs substantial delay as opposed to the LAN because the WAN is generally not as fast as the LAN.
Data Link Switching (DLSw) is a mechanism for forwarding SNA protocol frames over, e.g., a TCP/IP backbone WAN such as the Internet. In traditional bridging, the data link connection is end-to-end, i.e., effectively continuous between communicating end stations. A stream of data frames originating from a source station on a source LAN traverses one or more bridges specified in the path over the LLC2 connection to a destination station on a destination LAN. In a network implementing DLSw, by contrast, the LLC2 connection terminates at a local DLSw device entity, e.g., a router. An example of a DLSw network arrangement may comprise a host DLSw router connected to a host computer via a host LAN and a remote DLSw router connected to a remote LAN having a destination station. The LANs that are accessed through the DLSw routers may appear as SRB subnetworks attached to adjacent rings; each of these adjacent rings manifest as a virtual ring within each DLSw router that effectively terminates the SRB network.
FIG. 2 is a schematic block diagram of such a DLSw network 200 having a TCP/IP cloud 205 disposed between host and remote SRB subnetworks 202, 204. When communicating with the host as described above, the PU sends an INFO frame to which host responds with an RR frame. Because of the latencies introduced by the WAN cloud, however, a time-out condition may occur during this exchange. The DLSw network includes host and remote DLSw routers 1,2 that border the WAN cloud. These DLSw routers function as end points between TCP sessions over the TCP/IP cloud when transporting TR frames associated with LLC2 sessions over that intermediate network. DLSw switching may obviate the time-out problem introduced by the TCP/IP cloud by, e.g., having DLSw1 return a RR acknowledgment frame to the source end station (PU) upon receiving an INFO frame. Notably, the RR frame is returned prior to transmitting the native TR INFO frame over the TCP/IP network.
Broadly stated, each DLSw router establishes a xe2x80x9cpeer relationshipxe2x80x9d to the other DLSw router in accordance with a conventional capabilities exchange message sequence, and the logical and physical connections between these routers connect the subnetworks into a larger DLSw network. To establish a peer connection in accordance with an implementation of DLSw switching, the host DLSw router first opens logical TCP (Read/Write) xe2x80x9cpipexe2x80x9d connections to the remote DLSw router using a conventional socket technique to create a socket into the transport layer of the protocol stack. Once the TCP pipes are established, a Switch-to-Switch (SSP) Protocol is used to transport the capabilities exchange messages between the two DLSw routers.
The capability exchange messages contain various parameters, such as the number of pipes used for communicating between the DLSw routers and the largest frame size supported by the routers. Each DLSw router responds to each capability exchange message issued by its peer router with a capability exchange response message. Upon completion of the exchange, each router reconfigures itself to xe2x80x9cact uponxe2x80x9d the agreed capabilities and the peer connection is established. Establishment of a peer connection can occur automatically upon xe2x80x9cboot-upxe2x80x9d of each DLSw router; that is, as soon as a DLSw router activates, it connects with its DLSw peer. The DLSw forwarding mechanism is well known and described in detail in Wells et al. Request For Comment (RFC) 1795 (1995).
Upon receiving a TR frame from a source on the host SRB subnetwork that is destined for a destination on the remote SRB subnetwork, the host DLSw router employs the SSP protocol to communicate with its DLSw peer router by forwarding the native TR frame over the TCP/IP network to the remote SRB subnetwork. That is, the TR frame received at the host DLSw router from the source is encapsulated within a SSP protocol frame and forwarded over the TCP/IP cloud to the remote DLSw router. The source route information contained in the RIF of each TR frame terminates inside the virtual ring of the DLSw router; notably, the RIF information is locally stored at the DLSw router.
The host DLSw router then multiplexes the LLC2 session data stream over a conventional TCP transport connection to a remote DLSw router. LLC2 acknowledgment frames used to acknowledge ordered receipt of the LLC2 data frames are xe2x80x9cstripped-outxe2x80x9d of the data stream and acted upon by the host DLSw router; in this way, the actual data frames are permitted to traverse the IP cloud to their destination while the xe2x80x9coverheadxe2x80x9d acknowledgment frames required by the LLC2 connections for reliable data delivery are kept off the cloud. The LLC2 connections from the source LAN to the host transmitting DLSw router, and from the remote receiving DLSw router to the destination LAN, are entirely independent from one another. Data link switching may be further implemented on multi-protocol routers capable of handing DLSw devices as well as conventional (e.g., SRB) frames.
DLSw routers can establish multiple parallel TCP sessions using well-known port numbers. All frames associated with a particular LLC2 connection typically follow a single designated TCP session. Accordingly, SNA data frames originating at the PU are transmitted over a particular LLC2 connection along TR2 to DLSw 2, where they are encapsulated within a designated TCP session and transported over the TCP/IP cloud 205. The encapsulated messages are received by DLSw1, decapsulated to their original frames and transmitted over a corresponding LLC2 connection of TR1 to the host in the order received by DLSw2 from the PU.
The LLC2 connection between the PU and host is identified by a data link identifier (ID) 260 consisting of a pair of attachment addresses associated with each end station. Each attachment address is represented by the concatenation of a media access control (MAC) address (6 bytes) and a LLC service access point (SAP) address (1 byte). Specifically, each attachment address is classified as either a target address comprising a destination MAC (DMAC) and a destination SAP (DSAP), or an origin address comprising a source MAC (SMAC) and source SAP (SSAP) addresses. The attachment addresses are contained in the TRs frame exchanged between the PU and host entities.
Furthermore, the designated TCP session is identified by a pair of circuit IDs 270, each comprising a 64-bit number that identifies the LLC2 circuit within a DLSw circuit. The DLSw circuit ID generally comprises a data link circuit port ID (4 bytes) and a data link correlator (4 bytes). A pair of circuit IDs along with a data link ID uniquely identifies a single end-to-end circuit through the network. Notably, each DLSw router maintains a table 250 comprising a plurality of data link ID and corresponding DLSw circuit ID pair entries. In order to associate LLC2 frame traffic with a corresponding DLSw circuit when communicating over the IP cloud, each DLSw router typically indexes into the table (the xe2x80x9cDLSw tablexe2x80x9d) using a data link ID to find the corresponding DLSw circuit IDs.
The DLSw circuit information described above, including the data link IDs, are available to a network operator of a network management station (NMS) 280 via a Simple Network Management Protocol (SNMP) configured to access DLSw management information base (MIB) tables within the routers. The MIB and SNMP protocol, and their use in providing network management information between SNMP management stations and agents are well-known and described in, e.g., SNMP, SNMPv2 and RMON by William Stallings, printed by Addison Wesley Publishing Company, 1996.
The orientation of the MAC/SAP attachment addresses of the data link IDs acquired from each router is dependent on the proximity of the SNA entity to which the router is connected. For example, the remote DLSw router identifies the PU MAC/SAP attachment address as origin and the host network connection MAC/SAP attachment address as target, whereas the host DLSw router identifies the PU and host connection addresses in reverse order. The DLSw routers do not, however, maintain the name of the PU, which is a common way for an operator to identify a session.
A problem involving a PU session in the network 200 may be diagnosed by the network operator using a conventional approach that correlates SNA frame traffic sessions to DLSw routers for a network having only a single peer connection over an IP cloud between DLSw peer routers. According to this approach, the NMS communicates with an SNMP agent in each DLSw router to acquire DLSw MIB information including a data link ID identifying a DLSw circuit associated with the router. The NMS also issues commands to the host over a pipe connection 285 to retrieve the SNA-specific information from VTAM. Since the host computer xe2x80x9cownsxe2x80x9d SNA sessions in the network, it maintains SNA-specific information such as the PU name and the MAC/SAP addresses for the host network connection and the PU on a virtual telecommunications access method (VTAM) table in the host. The SNA-specific information retrieved from VTAM does not, however, include information with respect to the DLSw routers that are routing the session traffic.
In response to a query from the operator specifying a PU name of the session, the NMS compares the MAC/SAP addresses retrieved from VTAM with the data link IDs in the MIBs to identify a DLSw circuit at each router. The NMS then uses the orientation of the MAC/SAP attachment addresses from the routers to distinguish between the host and remote DLSw routers. Thereafter, the NMS can draw the topology of the DLSw network, including the DLSw circuit and PU session, to isolate any failures in the network.
A limitation of the conventional approach is that only a single set of DLSw peer routers may be xe2x80x9cdiscoveredxe2x80x9d, resulting in a partial description of the network. Rather than diagnosing a network having only a single DLSw peer connection, the present invention is directed to a more complicated network arrangement having multiple DLSw peer connection xe2x80x9chopsxe2x80x9d. The present invention provides tools that enable a complete view of the network having multiple DLSw peer connections. In particular, the present invention is directed to a technique for correlating SNA/IP information within a DLSw network having a multi-hop peer connection topology to enable drawing of a session and diagnosing of problems.
The present invention comprises a technique for efficiently correlating information pertaining to entities of a computer network having a multi-hop peer connection topology. The computer network is a data link switching (DLSw) network comprising multiple source-route-bridge (SRB) subnetworks interconnected by, e.g., Internet protocol (IP) clouds. The entities comprise System Network Architecture (SNA) host mainframe (xe2x80x9chostxe2x80x9d) and physical unit (PU) entities, along with DLSw routers. A DLSw peer connection is established between a local DLSw router and its remote xe2x80x9cpeerxe2x80x9d DLSw router over each IP cloud; each DLSw peer connection comprises DLSw circuits that are identified by, inter alia, data link identifiers (IDs) comprising attachment addresses of the host and PU entities.
The DLSw network environment is managed by a network management station (NMS) configured to communicate with the DLSw routers using a simple network management protocol (SNMP) to acquire the IP-specific information for storage on a management information base (MIB) database of the NMS; in addition, the NMS communicates with the host over xe2x80x9cpipexe2x80x9d connection to retrieve the SNA-specific information for storage on a VTAM database of the NMS. In accordance with the inventive technique, the NMS correlates the SNA-specific information with the IP-specific information to draw the multi-hop network topology to assist in problem isolation. As a result, the NMS can interactively access the DLSw routers while also obtaining address information about the SNA entities in the network.
The SNA-specific information includes media access control (MAC) and service access point (SAP) addresses of the host and PU entities, along with source routing information, hereinafter referred to as a xe2x80x9crouting information field (RIF)xe2x80x9d, associated with a SRB subnetwork coupled to the host. This information is preferably stored on a virtual telecommunication access method (VTAM) table of the host coupled to the network. On the other hand, the IP-specific information collected from each DLSw router includes (i) origin and target attachment (MAC/SAP) addresses of a DLSw circuit associated with the router, (ii) a circuit state of its DLSw circuit, (iii) a RIF, and (iv) an IP address of its peer DLSw router.
According to the invention, the technique involves determining the number of peer connection (DLSw circuit) xe2x80x9chopsxe2x80x9d in the network by matching data link IDs stored on the MIB database with the MAC/SAP addresses of the host and PU entities retrieved from the VTAM database. As noted, each data link ID comprises origin and target attachment (MAC/SAP) addresses of a DLSw circuit associated with each router; the order of these addresses is dependent on the proximity of the SNA entity connected to each router. For example, the remote DLSw router of each peer connection identifies the MAC/SAP addresses of the PU as its origin attachment address and the MAC/SAP addresses of the host network connection as its target attachment address; the host DLSw router of that peer connection identifies the PU and host connection addresses in reverse order. Thus, each host (and remote) DLSw router of each peer connection hop will have a matching set of origin and target attachment addresses (or data link IDs) and the number of matching sets equal the number of peer connections.
Once the number of DLSw circuits have been identified, the technique proceeds to verify that the circuits have the same status. The DLSw circuits generally have the same status as the data traffic (PU session) they service; thus, if the PU session is active, all DLSw circuits are active and if the session is inactive, all the circuits are inactive. If one of the circuits is inactive while another is active, the network topology may include an alternate path that the session traversed through the DLSw network. According to this step of the technique, the status of each DLSw circuit is determined by examining its circuit state (active or inactive) stored in the MIB database. To ensure the state information is up-to-date, each router may be xe2x80x9cdemand-polledxe2x80x9d for its IP-specific information, rather than retrieving the information from the MIB database.
Upon validating the active state of each circuit, the inventive technique proceeds to determine the order of the DLSw peer routers. As noted each host (and remote) router associated with each DLSw circuit maintains a similar PU and host orientation, but it may be unclear as to which circuit, and thus which pair of routers, is closer in proximity to the host (or to the PU). Such order determination is accomplished by examining the local RIF acquired from each router.
The RIF contains source route information in the form of ring number/bridge number tuples within a path between the stations. In a SNA session traversing a single DLSw circuit, there is a RIF between the remote router and the PU, and a RIF between the host router and the host network connection. If the session traverses two DLSw circuit hops, there is a first RIF between a first host router of a first circuit and the host network connection, a second RIF between the first remote router of the first circuit and a second host router of a second circuit, and a third RIF between a second remote router of the second circuit and the PU. It should be noted that the second RIF may also be calculated from the second host router to the first remote router wherein only a direction bit in the RIF differs. According to the invention, the matching second RIF informs the NMS that the two DLSw routers (i.e., the second host and first remote routers) storing that RIF are coupled together.
The RIF values are provided by the DLSw routers as part of the IP-specific information collected by the NMS. The host (VTAM) also maintains RIF information pertaining to its own host network connection with the first host router; this latter information may be useful to identify the first host DLSw router.
Once the order of the DLSw peer routers is determined, the topology of the DLSw network may be drawn, illustrating the relationship between the DLSw router and the SNA entities of the network. Such correlation allows the NMS to manage relationships between the entities for purposes of, e.g., activating/deactivating those entities and monitoring SNA frame traffic encapsulated within IP protocol packets. In addition, the inventive correlation technique may be used for troubleshooting operations to identify associations between specific DLSw and SNA entities, and to generally view dependency relationships between such entities in the integrated network environment.